NEAR-SHORE BATHYMETRY AND REEF BIOTOPES OF HENDERSON ISLAND, PITCAIRNGROUP

The coral reef which surrounds two thirds of Henderson Island, Pitcair n Group, consists of a reef aat, reef margin and fore-reef which slope s gradually into deeper water. The range of sublittoral habitats provi ded by this topography is limited, reflecting a low level of coral div ersity. Spur and groove formations of the fore-reef are present around the northern end of the island which contrasts with the south-western corner, where, in the absence of a hinging reef platform, subaerial c liff faces are fronted by a cliff foot submarine 'trench'. In general, live coral cover on the fore-reef was estimated at between 10-30%, th ough at sites off the east coast it reached 80%. The associated commun ities, particularly of sessile filter-feeding groups, were found to be impoverished. The two factors of biogeographical isolation and of loc al bioerosion processes are proposed as being the main reasons for the depauperate nature of the island's reef. Brief notes are included on the lagoon and fore-reef bathymetry and habitats of Ducie and Oeno Ato lls for comparative purposes. (C) 1995 The Linnean Society of London